Brake lining and method of making same



Patented Sept. 23, 1952 Julius E. Underwood and Alfred Hirsch, PainesvilIe, -O1iio, assignors to Diamond Alkali Company, Cleveland-,Ohio, a. corporation of- Dela- No Drawing. Application October 20-, 1949,, Serial No. 122,582

Glaims. 1

This invention relates to compositions ofmatter comprising siloxa-nes; and more particularly relates to compositions of matter comprisingsiloxanes and organic and inorganic additives which render the compositions especially suitable as friction elements, such as clutchfacings, brake linings", and the like. The term" friction el'ement, as used herein, is intended to mean a trio tional energy absorbing member of an energy transfer mechanism for accelerating or decelenating-motion in a mechanical system;

It has; heretofore been broadly suggested that siloxanes, particularly the" resinous siloxanes, are suitable as" bonding materials'infriction element compositions, principally because of' their oil, grease, and heat resistance; Investigationhasshown, however, that not all or even many of the various types. of. resinous siloxanesyare suitable for such purposes, especially since much more than mere. oil, grease,j. and heatresistance is required of the bonding material in'a'f'riction element. Moreover, it has been found by investigation that the. efiectiveness of even the: most suitable siloxane materials in such compositions tions of matter, the principal ingredientsof which include a cohydrolyzate of a mixtureof "1-0 mol per cent of an ethyl silicon trihalide and 70-90 mol per cent of a. phenyl' silicon trihalide, suitably about 20 mol per cent of the former and 80 mol per cent of the latter, a physical mixture of lead sulfate and lead monoxide, and asbestos either in the form of fiberstor in the form-ofa web, such as paper or cloth.

The mixtures of phenyl and ethyl silicon trihalides from which theco hydrolyzates used'as bonding agents in the compositions of the present invention are derived mayice-obtained fromany of the several phenyl or ethyl silicon trihalides but are preferably mixtures of phenyl' and ethyl silicon trichlorides, since these latter compounds are somewhat more economically producedthan 2 the other halide derivatives, particularly we phenyl and ethyl silicon tribromides: ortriiodides, and are more amenable to hydrolysis than: the phenyl and ethyl silicon trifiuorides. The: cohydrolyzate of a mixture ofthese two compounds in the proportionsstatedis readily obtained; by methods well-known inthe art, suchas by: combining the desired molar proportionoi each. at the preferred organosilico-n chlorides a. suit.- able non-aqueous solvent and adding the solution of the mixture to an aqueous-medium, which may contain in addition to the water therein, other organic or inorganic materials which tend to control the rate of the hydrolysis reaction. The co-hyd-rolyzate of themixture of organosilicon trihalides may then be-separated from the hydrolysis reaction mass in solutionby ordi nary: gravity separation of the aqueous and nonaqueous phases. The co-hyd-rolyzatesolution, or the resinous co-hydrolyzate obtained by evaporation of thesolvent therefrom, may be used" in compounding'the' compositions of the present invention. The amount of cG-hydrolyzate to be employed in these compositions may be varied over a wide range and is between about5 to 25% of. the total weight'of a composition, preferably within the range of 10% to- 20% of the total weight of a composition. The particular sequence of steps. employed in each of these techniques will be described more fully hereinafter.

The physical mixture of. lead sulfateand' lead oxide employed in the compositions of the present invention is obtained by combining finely divided lead sulfate and finely divided lead'oxide in suitable proportions. The fineness of the particles of these compounds is suitably of the order of 100-300 mesh, preferably" of the order of 200-300 mesh. The: compounds may be mixed in molar ratios of PbSOnPbO within the range of (lid-11:1, preferably, however, Within the range of 028-1041. The: mixture of PbSOr. and P100 is advantageously used. in amounts ranging. from 25% to of the total weight ofithe.

compositions.

Asbestos-isemployedin the compositions of the present invention in amounts ranging from 20%;

such that none is retained on a screen having 0.5" openings, approximately 75% is retained on a 12 mesh screen, and the remaining 25% passing the 12 mesh screen is retained on a 16 mesh screen, are especially suitable in the compositions of the present invention when used in amounts ranging from 20% to 50% by weight. A commercial grade representative of this type is manufactured by the Johns-Manville Company and available as their grade -K. In addition, it has been found that Webs of asbestos fibers, such as asbestos paper or woven asbestos cloth, generally ranging from 501% to 75% of the total Weight of the compositions, further increase the tenacity and improve the friction properties of molded articles obtained from the compositions of the present invention. For example, it has been found that when asbestos Webs, impregnated with a dispersion of the combination comprising a co-hydrolyzate of phenyl and ethyl silicon trihalides, and a mixture of lead sulfate and lead oxide in the molar proportions given above, are compressed under a pressure of approximately 4000 pounds per square inch, there results a molded article having a very low wear rate and a relatively high and constant coeincient of friction at high temperatures.

Small amounts, of the order of 2% to of the total weight of the compositions, of heat resistant synthetic elastomeric polymers and copolymers, for example, copolymers of the butadiene-acrylonitrile type which are commercially available under the trade-name Hycar, from the B. F. Goodrich Company, may be included in the compositions of the present invention and such elastomeric polymers and copolymers apparently function as plasticizers for the siloxane component of the compositions, thereby decreasing the brittleness of the siloxane binder and increasing the tenacity of the molded compositions.

Graphite may also be incorporated, if desired, particularly when the compositions are to be molded into friction elements. The amount of graphite, when so used, is preferably of the order of 1% to 5% of the total weight of the compositions.

In order that those skilled in the art may better understand the nature of the compositions of the present invention and in what manner the same may be obtained, the following specific examples are offered. For consistency in comparing the compositions of the several examples, a cohydrolyzate of mol per cent of ethyl silicon trichloride and 80 mol per cent of phenyl silicon trichloride is used throughout as the siloxane binding material.

EXAMPLE 1 Formulation 260 parts of a 61.5% solution in isopropyl ether of the co-hydrolyzate of 80 mol per cent of phenyl silicon trichloride and 20 mol per cent of ethyl silicon trichloride, containing 1.6 parts of triethanolamine (condensation catalyst for the organo-silicon trihalide co-hydrolyzate).

Procedure The lead monoxide and asbestos are placed in a Day mixer (having eccentric contra-rotating masticating members), having a mixing chamber moved from the mixing chamber.

' wheel shaft.

which is jacketed for temperature control by means of steam and/or water. These dry materials are blended in the mixer at room temperature until a substantially uniform mix has been obtained. The solution; of the organo-silicon halide co-hydrolyzate is added to the thoroughly blended combination of lead monoxide and asbestos and the entire mass mixed until substantial uniformity is obtained, after which the solvent is evaporated from the mass by admitting steam to the mixing chamber jacket. After substantially all of the solvent has been evaporated, a pulverulent mass of the mixture is obtained and re- The substantially dry coherent particles of the composition are passed through a Wiley hammer mill, wherein the particles are comminuted to a maximum particle size of approximately 5 mesh. The particle size of the pulverized material is controlled by the size of the openings in a screen surrounding the pulverizing, chamber. The pulverized material is placed in a mold cavity having an arcuate longitudinal cross section, and a molding inch in thickness, 2 /2 inches wide, and 5 inches arc length on a 7-inch radius, is obtainedby molding at 360 F. and 4000 pounds per square inch pressure for a period ofone hour. At the end of this time, the mold is cooled to F. and the molded article removed from the mold cavity, placed in a curing mold having cavity contours of the same general shape as that of the cavityemployed in the initial molding operation, and cur'ed.for. a period of 16 hours at 500-525 F. The cured molding is cooled to room temperature and fixed to a brake shoe as a brake lining element of a small laboratory dynamome tor for testing.

The dynamometer comprises a rear brake assembly of an fInternationa-l K-5 truck equipped with International Harvester 14-inch diameter brake drums No. 95,2231-1 at each end of the fly- The [dynamomete'r is so driven as to simulate the energy eifect. (94,250 foot pounds) on onewheel of a 10-ton truck in decelerating from a speed of 45 miles per hour to a position of rest in 6 seconds. The cycle frequency from acceleration from a position of rest to top speed, braking to decelerate to a position of rest, and accelerating again is 35 seconds, except during periods for the removal of brake linings for wear measurements, etc. After 10-.15 35-second cycles, the brake drum temperature of the brake assembly generally reaches 400-550 F., occasionally as high as 650' R; good. evidence. exists that the actual surface temperature of the lining may go as high as 1400 F.

The coefficient of friction m in this and the other examples hereinafter is calculated from the formula:

Fztangential friction force Pzload on the brake shoe and the constants are derived from other formulae developed by analysis of brake members for the particular dynamometer assembly.

7 The coeflicients of friction noted in this and the following examples are'calculated from data taken during deceleration in a cycle or series of cycles, whereas the drum temperatures corresponding to these coefiicients of friction are Brake Drum Temperature; F. g FEEEE E Room Temperature T 0. 27 400 l 0. 31 645 l 0. 52

EXAMPLE 2 formulation 2163' iifaits b 273' parts of a' 61-15% solution inisopropyl ether of. the co'-hyd lyzate of" 80rmolperv cent of 'phenyl; silicon tr i oride andzo' inrolper cent ofetliyl' silicon trichloride .containing 1.6 parts of triethanolamine (condensation. catalyst? for the cohydrolyzate).

424 parts of asbestos fibers: (of the same grade as that used in Example l) Procedure H These ingredients are mixed together inlpre'e c-is'el'y the same Lnianner-i-as thatdescribed for the composition of Examplel and a. molded brakelining" 'element-"'obtained fiom this: composition. Test results 1 The calculated rate cfiwear per thousand cycles based; on; 11-5 cycle is -Q. 68. inch.

rn'rc'rronfcnz-mcmnmsmlcsr Ooeficient of Friction EXAMPLE 3 Formulation 425 parts-t basic leadsulfate (PbSOc-PbC')",

(approximately 300 mesh).

260 parts of a 61.5% solution in isopropyl ether of the co-hydrolyzate i-c5189: mol per cent of phenyl silicon trichlor e and 20 mol per cent of ethyl silicon tri'chl'oride, containing 1.6 parts of. triethanolamine; v(comflensation, catalyst for the: organoasilieon'. chloride. ce-ihydrolyzate) 2& 6 fpartsmf? asbestosi fibers (of the same grade. asithat used-iirnExampleiy.

1 Procedure.

method of combining. these; materials obtaining a molded friction element; therefrom is. carried out; precisely thezsame manner. as that described in Example 1 above.

t m Test'residts I: s

The calculated rate of" wearup'err thousand cycles based on 352 cycles is 0.17 inch;

lead sulfate (seem; "mately .300 v friction. element as. deseribed".i 'n"Examp 'alsoemployed.

' "FRICTIONCEARACTERZESTICSTL Brake'Drum-Temperature;Fz I 3 Room Temperature I 425 EXA PLE 4 v v Formulation 2443 parts "of lead sulfate. (approximate! mesh). 1 i s 180 parts of lead monoxide (approximately 300 mesh) I 260 parts of a;-61.5-% solution in: isopropyL-ether otthc.co-hydrolyzate-of mol: percent oirphenyl silicontrichloride-and20-mclpercent cf ethl silicon. trichloride; containing-z 1.6? parts of ;trrethanolamine (condensation catalystfothe e gane-silicon trihalide; co.hydrclyza;te-)

- 216 parts of asbestesrfibers (of thers amegir as'that used in Examplel).

Proced ufeQ The ingredients of this iormulaarefcomb' in precisely the same manner as that descrih Example 1 and the method ofobtaining a1 l-eTesti'eswl ts; viv

The calculated rateoftzearip ar -awn basedon 800 cy cles. isl).0l2 inch f Fulcrum cnAn cTEn sTrosff P Brake Drum Temperature; F. g ggg .Room Temperatureilnn l :s L-l 034 500 0. 48 635 0. 45

EXAMPLE 5 Formulation I 17 6.5 parts ofthe dry comminut'ed' partially cone densed co-hydrolyzate-of amixture of 80 mol percent of phenyl silicon trichlorideand 20 mol per cent of ethyl siliconrtr ichloride.

25.5 parts of the but ne-acrylonitrile elastomcric 'copolymerav ai lable'under the tradename Hycar. 0.6 part sulfur.

ocedure The butadiene acrylonitrile 'copolyniexfi i's milled on. a rubber'mill having aroll'speed differential of 2-3 until, asubstantiallyecntmuou's sheet thereof is obtained; The mil-ling of, the butadiene-acrylonitrile copolymer is continued and the 76.5 parts.offthei-partially condensed cohydrolyzate added thereto and the milling continued until a substantially uniform mixture is obtained; after: which. the-:tsulfu'r is addedtas a curing catalyst for the b'utadiene-acrylonitrile elastomer, Thereaften. the. mixxis. removed f'rom the rubber mill as a substantially continuous sheet; which is: cooled. by means. of dry: ieeto. a

temperature at whichljthe'massilbecemeszbrittle and readily friable. The cold brittle mass is placed in. a Wiley hammer mill and comminuted to a maximum particle size of approximately mesh.

Formulation 168 parts of lead sulfate (approximately 300 mesh).

132 parts of lead oxide (approximately 300 mesh).

198 parts of asbestos fibers (of the same grade as that used in Example 1) Procedure The lead sulfate-lead monoxide and asbestos fibers are placed in a Day mixer and mixed together in the manner described in Example 1 above until a substantially uniform mixture has been obtained, after which the comminuted resinous mixture of Hycar, partially condensed siloxane resins, and triethanolamine is added to the batch during the mixing operation and the mixing continued until the mixture is uniform. Methyl ethyl ketone in an amount sufficient to wet the entire mass and render it plastic is added during the mixing operation in order substantially to coat'allof the particles of the dry inorganic materials with a solution of the resinous material. driven from the batch in a manner described in Example 1 and the pulverulent mass thus obtained comminuted in a Wiley hammer mill to a maximum particle size of approximately 5 mesh, from which c'omminuted mass a friction element is obtained by molding in accordance with the technique described in Example 1.

Test results The calculated rate of wear per thousand cycles based'on 2000 cycles is 0.0068 inch.

FRICTION CHARACTERISTICS Brake Drum Temperature, ll. of Friction Room Temperature Q 425 EXAMPLE 6 Formulation Thereafter, the solvent is v Procedure Precisely thesame procedure as that described in Example 5 is followed in this example to obtain a molded friction element.

Test results The calculated rate of wear per thousand cycles based on 2100 cycles is 0.005 inch.

FRICTION CHARACTERISTICS Brake Drum Temperature, F. gfigffi EXAMPLE 7 Formulation Formulation 174 parts of lead sulfate (approximately 300 mesh).

132 parts of lead monoxide (approximatelySOO mesh). v,

180 parts of asbestos fibers (of the same grade as that used in Example 1).

12 parts graphite.

Procedure A cured friction element is obtained in precisely the same manner as that described in Example 5 above.

I Test results The calculated rate of wear per thousand cycles based on 2000 cycles is 0.007 inch.

1 FRICTION CHARACTERISTICS Brake Drum Temperature, F. of Friction Room Temperature 0. 27 420 0. 50 l]. 47

of ethyl silicon trichloride, containing 0.6 part of triethanolamine (condensation catalyst for the co-hydrolyzate) mesh).

7.6 parts of graphite. 1 part sulfur.

peratures.

Procedure "l'he organza-"silicontrihalide oo-hyuroly zateand the Hycar? are dissolved in 400 rails. .of methyl ethyl ketone and the solution placed in a "vessel having "a propeller agitator inserted through a liquid tight bearing at "the bottom thereof. The agitator is set in motion and the combination of lead sulfate leafd monoxide,

graphite, andsulfur are added to the agitated solution in small increments Over a period "of approximately 10 minutes, after which ani'additi-onal 50 mls. 'of1methyl ethylxketonfare"added. 205 grams of asbestoscloth in theforrn of '18 strips, 2 inches by 5 inches fiarddippe'dinto-"the agitated suspension,- removed therefrom, dried and dipped a second time} remoyedand "dried. The gain in weight-ofthe lSStriDS" is 185 grains. The resin impregnated st-rips are assembledfin the form of a lamination and placed in them-old described iii-Example l --andmoldedand cured in based On 51f0,'00'0,'cy'cles' is 0,0072 inch. 7 L

' rnrotr roxf'cnllnii c'rnnrsrrcs BrakeDrum Temperature; F. I Room Temperature H 0.57 550 0. 40

Discussion'of results It will be observed from the above examples that when lead monoxide is used in combination with the siloxane material and asbestos (Ex ample l), the friction element obtained therefrom exhibits an increase in the coefficient cf friction-with increase of -temperature, whereas the composition containinglead sulfate in combination with'the siloxane material and asbestos (Example 2) exhibits a decrease in the coefficient of friction with increase of temperature, and that basic lead sulfate (PbSOr-PbO) in the combination (Example 3) gives a substantially constant coefiicient of friction over a wide range of tem- However, it will also be observed that in all three of these compositions, the calculated rate of wear per thousand stops is too high for a commercially acceptable friction element.

A comparison of the formulations and the test data of Examples 4-8, all of which include physica1 mixtures of lead oxide and lead sulfate, show that the combination of a co-hydrolyzate of a phenyl silicon trihalide and an ethyl silicon trihalide with asbestos and a mixture of lead sulfate and lead monoxide in a molded friction element possesses greater wear resistance, heat stability, and a more constant coefficient of friction over a wide temperature range than do similar combinations containing lead sulfate without lead monoxide, or lead monoxide without lead sulfate, or those containing basic lead sulfate (PbO-PbSOr) A further comparison may be made of thetest data given in Examples 4-8, inclusive, with data obtained from commercial brake linings functioning in the same dynamometer as that used in the above examples, and under substantially the same conditions, by referring to the data set forth in the table below:

Calculated Y (Heavy Duty) 10, 000

These data clearly show the superiority of the compositions of :-the present inventionover com- .mercially available brake linings, particularly in respect'to the rate of wear and the 'coefiic'ientrof friction at sustained high temperatures;.-1:Com-,

mercial brake linings initially exhibit arelatively high coefficient of frictionat low temperatures; which rapidly diminish, as shownby the above table of data, in some instances to zero FattJsustained high temperatures, while-friction- :elements manufactured from the compositions of .the presentinventionexhibit the inverse offlthi's behavior in that the friction elementsmade therefrom exhibit an increasein the coeffi'ci'ent of friction with increasing temperature to z-a maximum, after which at su'stainedhightem- ,peratures the 'c'oefilcient remains substantially constant 2 at a value greater than that :exhibited by prior art friction element compositions fat low temperatures.

Also of importance to the compos'itionsof. the present invention, although :somewhat. less dramatically demonstrable, is the extended transient thermoplastic :range .of the particular :00- hydrolyzates employed. herein; Thus, Zoo -by"- drolyzates of a mixturev of 70-90 mol percent ofaphenyl silicon trihalide and 10:30 m'c'aliper cent Of an ethylsilicon trihalide areeininently suited to the manufacture, of pressur'e m'old'ed friction elements, especially sincentheyaretschar acterized by remaining fluid throughoutthepressure molding operation. This is true whether theyv are recovered from the, hydrolysis reaction mass as a solution and. then compoun'dedwith the other ingredients of, the v. compositio'n or whether they are recovered as ,pulverulent: solids from such solutions by evaporation of the sol-'- vent and subsequently compounded. Thereafter,- the co-hydrolyzate material may be set or cured in a relatively short time and at moderate temperatures to a hard cohesive infusible bond between the particles and fibers of the inorganic portion of the compositions.

While there have been described various embodiments of the invention, the methods and products described are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the in- J form its principle I vention broadly in whatever may be utilized.

What is claimed is:

l. A composition of matter, the principal ingredients of which are asbestos, a co-hydrolyzate of a mixture of 10-30 mol per cent of an ethyl silicon trihalide and 70-90 mol per cent of a phenyl silicon trihalide, and a physical mixture of PbSO4 and PhD.

lesser ingredients of which include graphite.

4. A composition of matter, the principal ingredients of which amount to 90-100% thereof and consist essentially of a co-hydrolyzate of a mixture of 10-30 mol per cent of an ethyl silicon trihalide and 70-90 mol per cent of a phenyl silicon trihalide, PbSOi, PbO, and asbestos, and the lesser ingredients of which amount to up to 10% thereof and include graphite and an elastomeric copolymer of butadiene and acrylonitrile.

5. A friction element composition comprising -25% by Weight of a oo-hydrolyzate of a mixture of -30 mol per cent of an ethyl silicon trihalide and 70-90 mol per cent of a phenyl silicon trihalide, -75% by weight of asbestos, -60% by weight of a mixture of PbSO4 and PbO having a molar ratio of PbSO4:PbO within therange of 0.4-1.1:1, and up to 10% by weight of graphite and an elastomeric copolymer of butadiene and acrylonitrile.

v6. A: friction element composition comprising 5-25% by weight of a co-hydrolyzate of a mixture of about 20 mol per cent of an ethyl silicon trihalide and about 80 mol per cent of a phenyl silicon trihalide, 20-75% by weight of asbestos, 25-60% by weight of a mixture of PbSOi and PbO having a molar ratio of PbSO-lZPbO within the range of 0.4-1.1:1, and up to 10% by weight of graphite and an elastomeric copolymer of butadiene and acrylonitrile.

,7. 'A friction element composition comprising 10.9% of a co-hydrolyzate of a mixture of about 20 mol per cent of an ethyl silicon trihalide and about 80 mol per cent of a phenyl silicon trihalide, 52.9% of asbestos cloth, 14.5% PbO, 18.1% PbSOi and 3.6% of an elastomeric copolymer of butadiene and acrylonitrile.

8. The method of making friction elements which includes the steps of dipping asbestos cloth in a slurry of a co-hydrolyzate of a mixture of 10-30 mol per cent of an ethyl silicon trihalide and -90 mol per cent of a phenyl silicon trihalide, lead oxide, and lead sulfate in a solvent, drying said cloth, redipping said cloth in said slurry, redrying said cloth, assembling a plurality of said dipped dried clothes into a laminate and molding said laminate to obtain a friction element.

9. The method of making friction elements which includes the steps of impregnating asbestos cloth with a co-hydrolyzate of a mixture of 10-30 mol per cent of an ethyl silicon trihalide and 70-90 mol per cent of a phenyl silicon trihalide, lead oxide, and lead sulfate by dipping said cloth in a mixture of said co-hydrolyzate, said lead oxide, and said lead sulfate in a solvent, drying said cloth, assembling a plurality of said dipped dried clothes into a laminate and molding said laminate to obtain a friction element.

10. The method of making friction elements which includes preparing an intimate phyiscal mixture of lead monoxide, lead sulfate, and asbestos, combining therewith a solution of a cohydrolyzate' of a mixture of 10-30 mol per cent of an ethyl silicon trihalide and 70-90 mol per cent of a phenyl silicon trihalide in a solvent, mixing until substantial uniformity is obtained, while evaporating the solvent, placing said material in a mold cavity and molding said material under heat and pressure.

JULIUS E. UNDERWOOD. ALFRED HIRSCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Oct. 5, 1948 

2. A COMPOSITION OF MATTER, THE PRINCIPAL INGREDIENTS OF WHICH ARE ASBESTOS, A CO-HYDROLYZATE OF A MIXTURE OF 10-30 MOL PER CENT OF AN ETHYL SILICON TRIHALIDE AND 70-90 MOL PER CENT OF A PHENYL SILICON TRIHALIDE, PBSO4, AND PBO, AND THE LESSER INGREDIENTS OF WHICH INCLUDE AN ELASTOMERIC COPOLYMER OF BUTADIENT AND ACRYLONITRILE. 